Radioactive power supply system



June 11, 1963 E. G. LINDER 3,093,788

' RADIOACTIVE POWER SUPPLY SYSTEM Filed Aug. 26, 1955 i 2 Sheets$heet 1IN VEN TOR.

June 11, 1963 E. G. LINDER 3,093,783

RADIOACTIVE POWER SUPPLY SYSTEM Filed Aug. 26, 1955 2 Sheets-Sheet 2 f/5' Z kz/ PIT O Q EV Unite States Patent 3,093,788 RADIGACTEVE PUWERSUPPLY SYSTEM Ernest G. Linder, Princeton, N..l., assignor, by mesneassignments, to the United States oi America as represented by theSecretary oi the Air Force Filed Aug. 26, 1955, Ser. No. 530,863 3Claims. (Cl. 322-2) This invention relates generally to an improvedelectrical power supply system. More particularly, but not exclusively,the invention relates to an improved radioactive primary power sourcefor supplying electrical energy for the operation of electricalequipment, for example on guided missiles and rockets.

It is well known that weight considerations severely limit theconstruction and design of electrical power supply systems for highaltitude crait such as guided missiles and rockets. The velocity andrange of such craft are appreciably affected by small variations in theoverall mass.

Known radioactive primary voltage sources comprise essentially aradioactive emitter and a collector. Two of the 'difliculties ofoperating such sources with large amounts of emitter material are theexcessive generation of heat at the collector and the eventualdestruction of the collector due to radiation damage.

It is therefore an object of this invention to provide improved methodsand apparatus for radioactively generating electrical energy whichobviate the collection of the radiated charged particles.

Another object of the invention is to provide an improved electricalpower supply system for guided missiles and the like which does not addappreciably to the weight of the missile.

Another object of the invention is to provide an improved electricalpower supply system of reduced mass, which is capable of supplying apredetermined substantially constant potential and especially useful forhigh altitude apparatus and craft.

These and other objects and advantages of the invention are attained bya system comprising a radioactive charged particle radiator ofrelatively small size which is connected through a load (or workcircuit) to a body of much larger relative size. Such a system may beprovided in an electrically non-conductive non-ionizable medium. Whenthe system is located in a readily ionizable medium the ions produced byradiation should be prevented from establishing a conductive path fromthe radiator to the relatively large body. It is essential that the onlypath of electrical conduction between the radiator and the large body hethat which is established through the work circuit. The chargedparticles from the radioactive emitter are radiated into the mediumadjacent the radiator. In the case of a missile, for example, at a highaltitude where a practical vacuum exists, a small portion of themissiles hull is completely isolated from the remainder of the craftexcept for a connection to the remainder of the missile through theequipment and devices or circuits to be energized. Charged particles,such as beta-particles, are released from this small portion into thespace surrounding the missile. The departure of the charged particlesfrom the isolated portion results in the building up thereon of apotential of polarity opposite to that of the released chargedparticles. Due to the charge re-distribution on the missile as a whole,electrons will flow from the remainder of the missile toward thepositively charged portion through the only electrically conductive paththerebetween, namely, the work load. The potential difference acrossthis load will be according to Ohrns law, V=Ri, where R is the loadresistance and i is equivalent to the radioactive current released fromthe isolated portion into space. At

low altitudes where a relatively dense and ionizable medium around themissile may be expected, special precautions must be taken to preventionization of the surrounding gas by the radioactive emission fromestablishing a conductive path from the isolated portion to theremainder of the missiles hull. 'To do this the direction of radiationmust be such as to preclude the formation of an ion cloud ahead of themissile and the velocity of the missile must be greater than thevelocity of the ions formed.

The invention will be described in greater detail with reference to theaccompanying drawings in which:

. FIGURE 1 is a partially schematic view of one embodiment of theinvention; 7

FIGURE 2 is an elevational view of a guided missile partially in sectionand partially schematic, embodying the invention;

FIGURE 3 is a plan view of a guided missile as shown in FEGURE 2embodying the invention;

FIGURE 4 is an elevational, sectional fragmentary view of details of theembodiment of the invention as shown in FIGURE 2;

FIGURE 5 is a schematic diagram of the embodiment of the invention in amissile as shown in FIGURE 2;

FIGURE 6 is a schematic diagram of another embodiment of a power supplysystem according to the invention; and

FIGURE 7 is an elevational view, partially in section, partiallyschematic, of still another embodiment of the invention.

Similar reference characters are used throughout the drawings todesignate the same or similar parts.

Referring to FIGURE 1, a small electrically conductive body 1 ofrelatively low electrical capacity is connected by the conductor 2 to alarge body 3 of relatively high electrical capacity through a workcircuit 4. The bodies 1 and 3 are shown as spheres for convenience ofillustration only, and such shape is not critical or necessary foroperation according to the invention. The small sphere is coated orotherwise in contact with a relatively large amount of radioactivecharged-particle-emitting material 5. The radioactive material may, forexample be a beta particle emitter such as strontium 90. Preferably theradioactive material is of the purest quality so as to minimize theproblems arising from gamma ray emission from some impure radioactivematerial. The two spheres, the connection therebetween and the workcircuit are enclosed in a vacuum or other non-conductive non-ionizablemedium as indicated by the dash line 22.

Beta particles are emitted from the small radiator sphere l by theradioactive material. Assuming that just prior to such emission there isno potential difference between the large and small spheres, thedeparture of these particles results in the charging up positively ofthe small sphere. Hence as more and more negative particles leave thesmall sphere 1 a greater and greater positive charge will be built upthereon. The difference in potential between the small sphere 1 and thelarge sphere 3 will in turn result in a charge lfi-dlSlZllblltlOl'l inthe entire circuit as it seeks to return to and maintain the samepotential throughout. There will be an electron flow from all lesspositive points of the circuit or large sphere 3 to the more positivesmall sphere 1. This current must flow through the load 4 across which avoltage is thus developed.

Stated another way, the positive potential built up on the small sphere1 will result in a charge re-distribution in the entire circuit as itseeks to return to and maintain the same potential throughout. Thismeans that positive charges will be re-distributed throughout the small,relatively low capacity sphere 1, the large, relatively high capacitysphere 3, and the connection theres eaves between including the workcircuit 4. By employing a large, relatively high capacity sphere withthe work circuit between it and the low capacity sphere, more of thesecharges will flow into the large sphere and hence through the workcircuit 4. This is because the distribution of positive charges betweentwo bodies having electrical capacity is proportional to the ratio oftheir capacities, the larger the capacity the greater the aflinitythereof for charges. Thus if the electrical capacities of the twospheres were identical, only half the number of positive chargesdeveloped on the one would be distributed on the other. Hence byemploying a large capacity sphere as compared with the low capacity ofthe radiator sphere, a large proportion of the charges developed on thesmall sphere Will be distributed on the large sphere which acts as asink for these charges. Thus, for example, if the capacity of the largesphere is 100 times greater than the capacity of the small sphere, aboutthe same ratio of charges developed on the small sphere will flow to thelarge sphere. Preferably the capacity of the large sphere should beconsiderably greater than the total capacity of the load and smallsphere in order to pull the largest possible number or" chargesdeveloped on the small sphere through the load.

The current flow through the load thus is substantially equal to theradioactive current i emitted from the sphere 1 into space; hence thepotential difference generated across the load 4 is expressed by where Ris the load resistance. Since the load resistance and the current aresubstantially constant the potential diiference developed across theload will be substantially constant. This is true notwithstanding thefact that the system as a whole is developing an increasing positivecharge since negatively charged particles are lost therefrom and notreturned to the system.

Referring to FIGURE 2, a high-altitude craft 7 such as a guided missilehas an electrically-conductive hull 8. A portion 9 of the hull isisolated from the rest of the hull by means of any suitable electricallyinsulating material 10 such as porcelain or other ceramic material, forexample. Any suitable material may be used which is mechanically strongand temperature resistant. It is preferred that the isolated portion 9and the insulating material it be flush with the exterior portions ofthe hull for aerodynamic reasons. The exterior of the isolated portion 9is coated or otherwise provided with a radioactive material 11 capableof releasing or radiating charged particles into the space surroundingthe missile 7. In order to protect the radioactive material from theatmosphere and to insure its retention on the isolated portion 9 it maybe covered with a plastic material or metal foil to contain it is place.A suitable arrangement is shown in FIGURE 4 wherein the isolated portion9 is recessed below the main hull line and covered with the radioactivematerial 11 which in turn is covered with plastic material 12 which ismade flush with the hull 8 for aerodynamic reasons. The radioactivematerial :11 may alternatively be covered with metallic plating. Theprotecting covering for the radioactive material should be pervious toradiated charge particles. In this arrangement any radiation which isnot perpendicular to the flat radiating surface M of the isolatedportion 9 will strike the metallic side walls 16 and 16 which act asshields to prevent the radiation from reaching and possibly damaging orionizing the insulating material 10.

The radioactive material may be either a negative particle (beta)emitter or a positive particle (alpha) emitter according to theinvention. In the instant example, and for the purpose of explaining theinvention, a beta particle emitting material such as strontium 90 isemployed. This isolated charged particle radiating section is preferablylocated as near to the stern of the t missile as possible. Thisminimizes the possible formation of ion clouds due to the radiation withwhich contact by the missile is nearly unavoidable (as would be thesituation when the charged particle radiator is near the nose of themissile). Locating the radiator near the stern also enhances thepossibility of the complete escape of the radiated charged particlesfrom the isolated portion. The isolated portion 9 is electricallyconnected to the remainder of the hull 8 through the work circuit orload 4 and a switch 13 the purpose of which is explained in detailhereinafter. The circuitry of the power supply system described isschematically v shown in FIGURE 5.

Referring to FIGURE 5, the radioactive emitter will discharge or releasenegatively charged. particles into the space surrounding the missile 7.The departure of these charged particles will result in the isolatedportion 9' becoming charged to a polarity opposite to that of the chargeof the lost particles. Hence as more and more negative particles leavethe isolated portion 9 a greater and greater positive charge will bebuilt up thereon. The difference in potential between the portion 9 andthe remainder of the hull 8 will in turn result in a chargeredistribution in the entire circuit as it seeks to return to andmaintain the same potential throughout. There will be an electron flowfrom all less positive points of the circuit or hull 8 to the morepositive portion Q This current must flow through the load 4 acrosswhich a voltage is thus developed.

Thus the operation is substantially the same as the apparatus describedin connection with FIGURE 1. The

isolated portion 9 of the hull 8 corresponds to the small sphere ll; thehull 8 corresponds to the large sphere 3.

This process may be carried out at both high and low altitudes althoughspecial precautions must be observed when the missile is operating at alow altitude in a relatively dense ionizable medium. The chargedparticles being radiated into space will produce only a negligibleamount of ionization of any gas present around the missile due to therarity of the atmosphere at high altitudes. At low altitudes, however,the ionization of the air around the ship and especially in theneighborhood of the isolated portion 9 will result in an effectiveshort-circuit between the emitting portion and the adjacent portions ofthe hull 3. Thus to ope-rate the power supply system of the invention atlow altitudes or in an ionizable medium successfully, the direction ofradiation must be such as to preclude the formation of an ion cloudahead of the missile with which contact cannot be avoided. Preferablythe charged particles will be radiated in the backward direction asshown in FIGURE 7. In this embodiment the isolated portion 9 extendsabove the main hull 8 of the missile and has its fiat radiating surface14 facing the stern of the missile. The isolated portion in thisembodiment should be located Well toward the tail-end of the missile toenhance the possibility of avoiding shortcircuiting effects due toionization of the surrounding medium. Likewise such a location alsominimizes the collection by the missile of radiated charged particleswhose trajectory is such as to result in their returning to the radiatoritself thus reducing the net number of released charged particles.Collection of radiated particles by the remainder of the hull is notdetrimental and special provision for preventing such a return need notbe made. In fact the return of radiated particles to the missiles hullenhances the operation of the invention since negatively chargedparticles are supplied to regions from whence they are being pulled bythe positive potential being built up on the radiating portion 9. Theradiating portion is enclosed in an aerodynamically streamlined bubbleor dome 15 the rearward end of which is closed off for aerodynamicreasons by means of a gas-tight window d7 of material such as thin micawhich is transparent to charged particle radiation.

Though preferably the stream of charged particles is radiated in thebackward direction, a short-circuit may still occur between theradiating portion 9 and the adjacent portions of the hull 8 due toionization of the surrounding medium. This is explained by the fact thatsome of the ions formed by radiation will have a velocity of their ownwhich may be in the direction of travel of the missile. In such a casethe missile would not escape the ions formed and short-circuiting wouldoccur. To avoid this possibility the minimum velocity of the missilewhen in a dense ionizable medium must exceed the velocity of the ionsformed. This means that the missile must have a minimum velocity in thesupersonic range when in an ionizable medium.

When in an ionizable medium there will always be some return current, ito the radiating portion 9 due to ions, so that the above equationshould have a correction term added, and should read,

The direction of radiation is preferably in the backward directionespecially where the missile is at low altitudes where a dense ionizablemedium is to be encoun tered. However, radiation can be in a generallyforward or backward direction or at right angles to the direction oftravel of the missile. The more nearly the direction of radiationcoincides with the direction of travel of the missile, the greater mustbe the speed of the missile to escape the ions formed. Contact with ionsformed by radiation directly ahead of the missile cannot be avoided atall, hence radiation in this direction is undesirable ifshort-circuiting effects due to ion formation are to be minimized.

Thus by maintaining the missile velocity greater than the ion velocity,the missile can escape the short-circuiting effects of the ionization ofthe surrounding medium. With reference to FiGURE 1, this suggests that astationary system can be operated even when in an ionizable medium bycausing the ionizable medium to have a velocity in a direction away fromthe stationary apparatus which velocity is greater than the velocity ofthe ions themselves. This may be accomplished by blowing the air pastthe system at the requisite velocity.

Since the static charge on the missile increases as radiation continues,the high charge difference between the missile and the earth mightresult in some difiiculties if the missile were to abruptly return toearth and discharge itself. In general, however, descent through theatmosphere will result in slowly discharging the missile as it entersthe denser atmosphere. It is also possible to limit the charge developedaccording to another embodiment of the invention as illustratedschematically in FIGURE 6. In the example heretofore describednegativelycharged particles are radiated from the iolated portion 9 andthe missile as a whole charges up positively. The positive chargedeveloped can be limited to any predetermined value by radiatingpositively-charged particles into the space surrounding the missile.Thus if the number of positively-charged particles leaving the missileis equal to the number of negative particles leaving the missile, thepositive charge developed on the isolated portion 9 no longer increasesbut becomes constant or stabilized at the potential developed beforepositively-charged particle radiation commenced. If the number ofpositive particles radiated is less than the number of radiated negativeparticles, then the positive charge on the missile will continue toincrease but at a slower rate, depending upon the difference in thenumber of radiated particles. If the number of positive particlesradiated is greater than the number of radiated negative particles, thenthe positive charge on the missile will decrease. In this manner thecharge built up on the missile can be controlled and established at anypredetermined value.

The preferred means for discharging the missiles positive charge dependsupon the surrounding medium. When the missile is at high altitudes andin a relative vacuum it is preferred to release positively chargedparticles by radiation from a radioactive material such as polonium 210.The alpha particle emitting material 18 may be located upon anotherportion 19 of the missiles hull and isolated therefrom by means of a gapor the insulating portion 26. When the switch is in position A theradiation of beta particles from the isolated portion 9 will result inthe building up of a positive charge on the missile as describedpreviously. When this charge has reached the desired value the switch 13is thrown to position B so as to connect the alpha emitting isolatedportion 19 with both the rest of the missiles hull 8 and the betaemitting isolated portion 9. The departure of the positively chargedparticles from the portion 19 compensates for the departure ofnegatively charged particles from the portion 9 as explained previously.Furthermore, this compensation may be controlled so as to bring about astable charge on the missile, or to decrease the charge, or to permit aretarded charge increase as compared with a free-running chargeincrease.

When controlling the charge on the missile by emitting alpha particlestherefrom the same requirements on the direction of radiation asdescribed in connection with the emission of beta particles should beobserved. If, for example, the alpha particles were able to return tothe missile nothing would be accomplished by way of reducing thepositive charge thereon. If the missile is being char ed positively,then this positive charge will tend to repel alpha particles that mightattempt to return. This method of controlling the charge on the missilecan also be employed at low altitudes in a relatively dense ionizablemedium but further precautions, such as previously mentioned, must beobserved to prevent short circuiting due to ionization of thesurrounding gas. An arrangement such as described for the radiation ofbeta particles in a dense medium (shown in FIGURE 7) would likewiseovercome difficulties due to ionization by alpha particles in a densemedium.

An alternative method for discharging the positive charge is by thephenomenon of cold emission of positive particles. To accomplish this asharply pointed electrode is provided which may comprise the nose 21 ofthe missile as shown in FIGURE 2. The sharply pointed electrodeconcentrates a very intense electrical field at its point which arisesfrom the charge on the missile. This embodiment is, however, preferredwhen the missile is in a relatively dense ionizable medium. When in sucha medium the field at the point of the electrode 21 causes ionization ofthe surrounding gas and since the field potential is positive, negativeions or electrons will be attracted to the electrode from whence theywill redistribute themselves throughout the hull of the missile tocompensate for the positive charge being built up thereon.

It should be understood that a voltage may be developed across the workcircuit 4 whether either a positive or negative particle emitter isemployed. For example, the isolated portion 9 could become negativelycharged by having an alpha particle emitter located thereon. Since thisportion would gradually build up a negative charge greater than thepotential on other portions of the missile a charge re-distributionwould occur with the result that electrons would flow in the oppositedirection through the work circuit 4. Likewise, the negative portionbuild up on the missile would then be controllable by providing a betaparticle emitter elsewhere whose function and operation on the isolatedportion 19 would be the same as that described in con nection with theembodiment where the missile was being charged positively.

While according to the preferred embodiment of the invention the chargedparticle radiator comprises an isolated portion of the vehicles hull andthe equipment to be operated is connected between this portion and theremainder of the hull, the invention is not limited to this arrangement.The charged particle radiator could be an aerodynamically streamlinedelectrode extending from the hull of the craft-and suitably insulatedtherefrom. Likewise the load circuit could be connected between thecharged particle radiator and any suitable conductive mass within thevehicle into which the developed charge could flow. As pointed outpreviously, however, the electrical capacity of this conductive massshould be large as compared with the electrical capacity of theelectrode. Furthermore, as has been mentioned, the isolation of thecharged particle radiator could be accomplished by providing a gapbetween the radiator and the hull of the craft. At high altitudes theradiator would thus be electrically isolated by the relative vacuumconstituting this gap. At low altitudes the air itself is a sufficientlygood electrical insulator to provide the necessary isolation althoughthe special precautions against ionization referred to previously shouldbe observed.

As used herein and in the appended claims the term missile is intendedto describe any object or craft capable of travelling through space,Whether propelled by its own power or projected from the earths surface.

What is claimed is:

1. An electrical power supply apparatus consisting of first means havinga relatively low electrical capacity, second means electricallyinsulated from said first means and having a relatively high electricalcapacity, said first means being a small, electrically conductive bodyhaving a flat radiating surface for releasing charged particles of onepolarity into the space adjacent thereto, said charged particles havinga travel path perpendicular to said fiat radiating surface and away fromsaid second means, said charged particles escaping from said powersupply apparatus, the release of said particles producing an electricpotential of a polarity opposite to said one polarity on said firstmeans, said seconduneans being an electrically conductive body which islarge with respect to said first means, an electrical load, third meansconnecting said load beaween said first means and said second means,whereby current may flow between said first and said second means andthrough said load, and fourth means connected to said second means forcontrolling the static charge on said electric supply apparatus.

2. The apparatus of claim 1 wherein said fiat radiating surfacecomprises a radioactive source of beta-particles.

3. A radioactive power supply consisting of first and secondelectrically conductive bodies, said first body being small and ofrelatively low capacity, said second body being large with respect tosaid first body and of relatively high capacity, said first body beingelectrically insulated from said second body, said first body having afiat radiating surface of radioactive material for releasing chargedparticles of a finst polarity, the release or" said charged particlesproducing an electric potential of a second polarity on said first bodywith respect to said second body, a single path of electrical conductionbetween said first body and said second body, said path of electricalconduction consisting of: a load, a first connector connecting saidfirst body to one side of said load, and a second connector connectingsaid second body to the other side of said load, whereby current willflow between said first and said second bodies only through said load.

References Cited in the file of this patent UNITED STATES PATENTS2,517,120 'Linder Aug. 1, 1950 2,552,050 Linder May 8, 1951 2,709,229Linder May 24, 1955 2,728,867 Wilson Dec. 27, 1955 2,789,241 Frey Apr.16, 1957

1. AN ELECTRICAL POWER SUPPLY APPARATUS CONSISTING OF FIRST MEANS HAVINGA RELATIVELY LOW ELECTRICAL CAPACITY, SECOND MEANS ELECTRICALLYINSULATED FROM SAID FIRST MANS AND HAVING A RELATIVELY HIGH ELECTRICALCAPACITY, SAID FIRST MEANS BEING A SMALL, ELECTRICALLY CONDUCTIVE BODYHAVING A FLAT RADIATING SURFACE FOR RELEASING CHARGED PARTICLES OF ONEPOLARITY INTO THE SPACE ADJACENT THERETO, SAID CHARGED PARTICLES HAVINGA TRAVEL PATH PERPENDIUCLAR TO SAID FLAT RADIATING SURFACE AND AWAY FROMSAID SECOND MEANS, SAID CHARGED PARTICLES ESCAPING FROM SAID POWERSUPPLY APPARATUS, THE RELEASE OF SAID PARTICLES PRODUCING AN ELECTRICPOTENTIAL OF A POLARITY OPPOSITE TO SAID ONE POLARITY ON SAID FIRSTMEANS, SAID SECOND MEANS BEING AN ELECTRICALLY CONDUCTIVE BODY WHICH ISLARGE WITH RESPECT TO SAID FIRST